The field of the present invention relates to removable cartridge disk drives in general, and more particularly, to a removable cartridge disk drive and system which provides downward compatibility for removable cartridges of different disk storage capacities and characteristics.
Removable disk cartridges have been available on the market for some time. Unlike fixed disk drive systems, removable disk cartridge systems enable a user to easily replace a high capacity disk, allowing for convenient exchange of large amounts of information between remote sites and for greatly increased system storage capacity.
Removable disk technology continues to advance, providing the user with cartridges and disk drives of increasing performance and data storage capacity. These advancements are universally beneficial, leading to less cost per unit of data stored and enhanced accuracy of data storage and retrieval operations. Nevertheless, problems associated with technological advancement do occur. One of the most critical problems in the area of removable cartridge technology concerns upward and downward compatibility.
Because removable disk cartridges are by definition removable, they can be used interchangeably between one disk product and another. Thus, a removable cartridge originally designed for an older, lower-capacity disk drive can often be inserted in a newer, higher-capacity disk drive and data can be written on or read from the disk in the lower-capacity cartridge by the read/write head in the higher-capacity drive. However, after the higher-capacity drive writes on a lower-capacity cartridge, difficulties may occur when the re-written lower-capacity cartridge is reinserted back into the older, lower-capacity disk drive. One reason for this difficulty is that the read/write head width and associated track pitch of the higher-capacity disk drive are usually smaller than the head width and associated track pitch of the lower capacity disk drive. As a result, portions of the old data signals recorded in a given track by the lower-capacity disk drive remain in xe2x80x9csidebandsxe2x80x9d on either side of the data newly recorded in the higher-capacity disk drive, giving rise to a potential for interference when the lower-capacity disk drive performs read operations.
The sideband phenomenon is illustrated in FIG. 1A which depicts an A/B servo pattern recorded on a lower capacity removable disk cartridge over a localized track region. As can be seen from FIG. 1A, the recording data in a data track 2 of a removable cartridge originally designed for a lower-capacity disk drive, using a read/write head 4 of a higher-capacity disk drive, leaves inner and outer sidebands 6, 8 containing portions of the old data signals recorded in the data track by the (wider) read/write head (not shown) of the lower-capacity disk drive. If the removable cartridge with the new data recorded on it is subsequently removed from the higher-capacity disk drive and reinserted into the lower-capacity disk drive, these inner and outer sidebands will create interference during the read operation in the lower-capacity drive. Stray or random flux intervals in the sidebands will impact on the lower-density read/write head as it passes over the data recorded by the high-density head, leading to spurious or corrupted data readings.
Several techniques have been developed to remove sideband interference in lower-capacity removable cartridges containing data re-recorded with a higher-density read/write head. For example, a device receiving a disk, may perform a DC erase of the old data originally recorded on the lower-capacity disk by the first-generation, lower-density read/write head when new data is to be stored on the disk of lower-capacity cartridge using the higher-density read/write head. As shown in FIGS. 2A-2B, erasing may be accomplished by injecting a xe2x80x9cstaticxe2x80x9dor DC offset signal into the track following feedback loop of the disk device so as to reposition the smaller, high-density head over the inner and outer sidebands of each data track during erase operations.
However, difficulties may be encountered when using the prior art static offset technique to eliminate sideband interference when a higher-density head writes data over a lower-density data track. These difficulties are apparent upon consideration of FIG. 2C. As can be seen in FIG. 2C, application of the static offset to eliminate the sideband on either side of track centerline produces a constant state offset condition wherein the higher-density head is located along a region of the A/B servo feedback waveform unacceptably near the saturation region of the waveform. Small deviations from the optimum head offset position during the sideband erasing operation can move the head into the saturation region, resulting in no useful feedback, and, in effect, loss of some disk device functionality. In addition, the dc offset technique is time and processing intensive as the disk device is required to perform multiple erase passes. Further the erase passes greatly degrade performance of writing first-generation media on a second-generation drive.
From the foregoing it is appreciated that there exists a need for an apparatus and methods that allow for a performance-independent solution to the described problem. By having such an apparatus and method, true downward capability for older cartridges recorded in lower-capacity disk drives can be realized in higher-capacity disk drives.
The present invention provides a method and apparatus allowing first generation storage media to efficiently cooperate with subsequent generation storage media devices. When first generation storage media is first received by subsequent generate storage media devices, the subsequent generation storage media device reads the storage media for a specific stored signals having format information. Upon the detection of the stored signal format information, the second generation storage media device processes the stored signal format information to determine if the storage media is in accordance with the second generation storage media device format. If the format is in accordance, the second generation storage media device then performs storage media device operations on the media. The contrary being true, the second generation media device updates the stored signal format information such that the storage media becomes in accordance with the second generation storage media device.
In the event that an updated first generation storage media is placed in a first generation storage media device, the first generation storage media device updates the stored signal format information to make the storage media compliant with the first generation storage media device format. The first generation storage media device is then capable of performing first generation storage media device operations on the first generation storage media.
In both scenarios, any information found on the first generation storage media will be discarded by subsequent first or second generation storage media device operations.